Knowledge Bank

The vapor phase visible and ultraviolet absorption spectra of three diazanaphthalenes have received attention in the literature: cinnoline (1,2-), quinazoline (1,3-), and quinoxaline (1,4-). Furthermore, polarized absorption spectra of single and mixed crystals of phthalazine (2,3-diazanaphthalene) at $4.2\circ K$ have been reported. In each case the weak, lowest energy absorption region is assigned to $\pi \ast \leftarrow n$ transition(s), and the stronger bands at higher energies to $\pi \ast \leftarrow \pi$ transitions. We wish to report vapor absorption measurements on 1,5-diazanaphthalene; the first case in which the nitrogen atoms are on adjacent rings in this family of molecules. High resolution absorption spectra were photographed using a 55,000 lines/inch grating for the region $2700\backslash AA$ to $4000\backslash AA$. The $\pi \ast \leftarrow n$ system has an origin near $25,800cm-1$, with a strong prominent vibrational progression of $525cm-1$. The first $\pi \ast \leftarrow \pi$ system has an origin at $32.874cm-1$ and consists of broad diffuse bands with up to six members of a prominent progression of $700cm-1$. A vibrational analysis will be presented.